Lumpy Shoulders

So often, we think of the arms and shoulders when trying to correct topline. Setting/Rolling the shoulders back all happens in the back as LG and a couple of others have mentioned. Pulling the lats in and downwards is easy, actually. Relaxing the arms is th hard part. With the arms in a relaxed, lowered, and slightly rounded shape (first position), reach lightly down and outward as if scooping water from a basin. Lift the arms continuing to reach down/outwards. When the arms get to about chest level, slightly turn the palms inward as if to let the water pour out of the hands.Notice how this naturally begins to open the embrace. Slightly part the arms to about the point where the hands are in front of the pecs. It is here that the shoulders want to start to rise up. Maintain the in/downward pull in the back, and only adjust the hold from the elbows. Hope it conveys as well here as it works in class. Bonne chance.

I have an interesting related problem, and I am wondering if anyone has any advice for it. For the most part, I am good at keeping my shoulders down (although have my moments like all), but what my pro has discovered is that I have dips in my shoulders when my arms are up--due to years of...well wearing bras to support a large chest. These dips get very pronounced when I put my arms up, even if I am not wearing a bra with straps over the shoulder, and the dips make it look like my shoulders are up, even when they are down.

Any suggestions for this? Perhaps ways to reinforce my dresses or something?

no clue...but I do have huge delts which also makes my shoulders look like they are up when they aren't...so I have to work
especially hard to relax...because when they really are up it looks twice as bad

No idea if this is helpful, but I find that my shoulders are in a better position when I think about my sternum, rather than obsessing over the shoulders themselves. And my shoulder position gets messed up when I try to keep my backline (elbow to elbow) "straight" in the sense of "parallel to the floor."